How do public companies raise additional funds?

I'm a startup CEO so I know how selling shares work. However, I am curious about publicly traded companies (e.g. on the NASDAQ). I understand that an IPO is where a companies goes public and sells shares to raise money. However, if a public company (post-IPO) wants to raise additional funding (above and beyond the IPO) by selling shares, how does it do so? For example, does the company have to announce publicly “in August we plan to sell an additional 10M shares” or can they do it secretly, or do they have to file an SEC form first, or is it forbidden for public companies to raise additional funds? I assume that public companies are allowed to raise additional financing by selling more shares, but I am very confused as to what are the mechanics of that transaction. Are there SEC forms involved? Is there time period they have to announce before being allowed to? Is there a limit to how many shares can be sold? Does the Board of Directors have to sign off on this transaction? How can I find out whether public companies are raising additional funds through selling more shares? Thanks in advance!